Chemoconvulsant model of chronic spontaneous seizures

Novel Catalytic Antioxidant Formulation Decreases Oxidative Stress, Neuroinflammation and Cognitive Dysfunction in a Model of Nerve Agent Intoxication

Reactive oxygen species have an emerging role in the pathologic consequences of status epilepticus. We have previously demonstrated the efficacy of a water-for-injection formulation of the meso-porphyrin catalytic antioxidant, manganese (III) meso-tetrakis (N-N-diethylimidazole) porphyrin (AEOL10150) against oxidative stress, neuroinflammation, and neuronal death initiated by kainic acid, pilocarpine, diisopropylflurophosphate (DFP), and soman. This previous dose and dosing strategy of AEOL10150 required smaller multiple daily injections, precluding our ability to test its efficacy against delayed consequences of nerve agent exposure such as neurodegeneration and cognitive dysfunction. Therefore, we developed formulations of AEOL10150 designed to deliver a larger dose once daily with improved brain pharmacodynamics. We examined four new formulations of AEOL10150 that resulted in 8 times higher subcutaneous dose with lower acute toxicity, slower absorption, longer half-life, and higher maximal plasma concentrations compared with our previous strategy. AEOL10150 brain levels exhibited improved pharmacodynamics over 24 hours with all four formulations. We tested a subcutaneous dose of 40 mg/kg AEOL10150 in two formulations (2% carboxymethyl cellulose and 4% polyethylene glycol-4000) in the DFP rat model, and both formulations exhibited significant protection against DFP-induced oxidative stress. Additionally, and in one formulation (4% polyethylene glycol-4000), AEOL10150 significantly protected against DFP-induced neuronal death, microglial activation, delayed memory impairment, and mortality. These results suggest that reformulation of AEOL10150 can attenuate acute and delayed outcomes of organophosphate neurotoxicity. SIGNIFICANCE STATEMENT: Reformulation of manganese (III) meso-tetrakis (N-N-diethylimidazole) porphyrin allowed higher tolerated doses of the compound with improved pharmacodynamics. Specifically, one new formulation allowed fewer daily doses and improvement in acute and delayed outcomes of organophosphate toxicity.

Alzheimer risk-increasing TREM2 variant causes aberrant cortical synapse density and promotes network hyperexcitability in mouse models

The R47H variant of triggering receptor expressed on myeloid cells 2 (TREM2) increases the risk of Alzheimer's disease (AD). To investigate potential mechanisms, we analyzed knockin mice expressing human TREM2-R47H from one mutant mouse Trem2 allele. TREM2-R47H mice showed increased seizure activity in response to an acute excitotoxin challenge, compared to wildtype controls or knockin mice expressing the common variant of human TREM2. TREM2-R47H also increased spontaneous thalamocortical epileptiform activity in App knockin mice expressing amyloid precursor proteins bearing autosomal dominant AD mutations and a humanized amyloid-β sequence. In mice with or without such App modifications, TREM2-R47H increased the density of putative synapses in cortical regions without amyloid plaques. TREM2-R47H did not affect synaptic density in hippocampal regions with or without plaques. We conclude that TREM2-R47H increases AD-related network hyperexcitability and that it may do so, at least in part, by causing an imbalance in synaptic densities across brain regions.

Multi-view image-based behavior classification of wet-dog shake in Kainate rat model

The wet-dog shake behavior (WDS) is a short-duration behavior relevant to the study of various animal disease models, including acute seizures, morphine abstinence, and nicotine withdrawal. However, no animal behavior detection system has included WDS. In this work, we present a multi-view animal behavior detection system based on image classification and use it to detect rats' WDS behavior. Our system uses a novel time-multi-view fusion scheme that does not rely on artificial features (feature engineering) and is flexible to adapt to other animals and behaviors. It can use one or more views for higher accuracy. We tested our framework to classify WDS behavior in rats and compared the results using different amounts of cameras. Our results show that the use of additional views increases the performance of WDS behavioral classification. With three cameras, we achieved a precision of 0.91 and a recall of 0.86. Our multi-view animal behavior detection system represents the first system capable of detecting WDS and has potential applications in various animal disease models.

Animal Models of Epilepsy: A Phenotype-oriented Review

Epilepsy is a serious neurological disorder characterized by abnormal, recurrent, and synchronous discharges in the brain. Long-term recurrent seizure attacks can cause serious damage to brain function, which is usually observed in patients with temporal lobe epilepsy. Controlling seizure attacks is vital for the treatment and prognosis of epilepsy. Animal models, such as the kindling model, which was the most widely used model in the past, allow the understanding of the potential epileptogenic mechanisms and selection of antiepileptic drugs. In recent years, various animal models of epilepsy have been established to mimic different seizure types, without clear merits and demerits. Accordingly, this review provides a summary of the views mentioned above, aiming to provide a reference for animal model selection.

The Kainic Acid Models of Temporal Lobe Epilepsy

Experimental models of epilepsy are useful to identify potential mechanisms of epileptogenesis, seizure genesis, comorbidities, and treatment efficacy. The kainic acid (KA) model is one of the most commonly used. Several modes of administration of KA exist, each producing different effects in a strain-, species-, gender-, and age-dependent manner. In this review, we discuss the advantages and limitations of the various forms of KA administration (systemic, intrahippocampal, and intranasal), as well as the histologic, electrophysiological, and behavioral outcomes in different strains and species. We attempt a personal perspective and discuss areas where work is needed. The diversity of KA models and their outcomes offers researchers a rich palette of phenotypes, which may be relevant to specific traits found in patients with temporal lobe epilepsy.

Epileptogenesis-induced changes of hippocampal-piriform connectivity

OBJECTIVE

Tissue remodeling has been described in brain circuits that are involved in the generation and propagation of epileptic seizures. Human and animal studies suggest that the anterior piriform cortex (aPC) is crucial for seizure expression in focal epilepsies. Here, we investigate the effect of kainic-acid (KA)-induced seizures on the effective connectivity of the aPC with bilateral hippocampal CA3 regions using cerebro-cerebral evoked potentials (CCEPs).

METHODS

Adult male Sprague-Dawley rats were implanted with a tripolar electrode in the left aPC for stimulation and recording, and with unipolar recording electrodes in bilateral CA3 regions. Single pulse stimulations were given to the aPC and CCEPs were averaged before KA injections and after the emergence of spontaneous recurrent seizures (SRS). Similar recordings at equivalent time intervals were obtained from animals that received saline injections instead of KA (controls).

RESULTS

In the experimental group, the percentage change of increased amplitude of the contralateral (but not ipsilateral) CA3 CCEPs between pre-KA injection and after the emergence of SRS was significantly greater than in controls. No significant single-pulse-induced spectral change responses were observed in either epileptic or control rats when comparing pre- and post-stimulus time intervals. Also, we found no correlation between seizure frequency and the extent of amplitude changes in the CCEPs.

CONCLUSIONS

In the KA model, epileptogenesis results in plastic changes that manifest as an amplification of evoked potential amplitudes recorded in the contralateral hippocampus in response to single-pulse stimulation of the aPC. These results suggest epileptogenesis-induced facilitation of interhemispheric connectivity between the aPC and the hippocampus. Since the amplitude increase of the contralateral CCEP is a possible in vivo biomarker of epilepsy, any intervention (e.g. neuromodulatory) that can reverse this phenomenon may hold a potential antiepileptic efficacy.

CREB Protects against Temporal Lobe Epilepsy Associated with Cognitive Impairment by Controlling Oxidative Neuronal Damage

BACKGROUND

Cognitive dysfunction as a common comorbidity of epilepsy often manifests as learning and memory impairments in patients with temporal lobe epilepsy (TLE). The pathogenetic molecular mechanisms underlying epilepsy-associated cognitive dysfunction are incompletely understood. We investigated the role of cAMP response element binding protein (CREB) and its downstream signaling pathways in the pathogenesis of cognitive impairment in mice with TLE.

METHODS

Plasmid vectors of CREB-specific short-hairpin RNAs and CREB cDNA were prepared and transfected into primary neurons. Neuronal apoptosis and mitochondrial oxidative stress were assessed by flow cytometry. For in vivo studies, TLE in mice was induced by pilocarpine injection, and TLE-associated memory decline was evaluated using the Morris water maze after treatment with the CREB inhibitor 666-15, with or without the mitochondria-specific antioxidant MitoQ. CREB and its downstream mediators were examined by Western blotting analysis and quantitative reverse transcription polymerase chain reaction.

RESULTS

CREB knockdown induced mitochondrial reactive oxygen species production and apoptosis in primary neurons whereas CREB overexpression brought the opposite effects. The TLE mice exhibited elevated oxidative stress and neuronal apoptosis with decreased expression of CREB and its downstream mediators including PKA, CaMKIV, arc, and c-fos. CREB inhibition exacerbated TLE-associated oxidative neuronal apoptosis and memory decline. MitoQ treatment restored the expression of CREB and its downstream mediators, and prevented TLE-associated oxidative neuronal damage and memory deficits aggravated by CREB inhibition.

CONCLUSION

CREB plays a significant role in TLE-associated oxidative neuronal damage and memory impairment. This novel finding provides the evidence of the relationship between CREB and mitochondrial oxidative stress and cognitive dysfunction in epilepsy. Mitochondria-specific antioxidants such as MitoQ may alleviate TLE-associated cognitive dysfunction through activation of CREB and its downstream signaling pathways.

Inhibition of human microsomal PGE2 synthase-1 reduces seizure-induced increases of P-glycoprotein expression and activity at the blood-brain barrier

The cause of antiseizure drug (ASD) resistance in epilepsy is poorly understood. Here, we focus on the transporter P-glycoprotein (P-gp) that is partly responsible for limited ASD brain uptake, which is thought to contribute to ASD resistance. We previously demonstrated that cyclooxygenase-2 (COX-2) and the prostaglandin E receptor, prostanoid E receptor subtype 1, are involved in seizure-mediated P-gp up-regulation. Thus, we hypothesized that inhibiting microsomal prostaglandin E₂ (PGE2) synthase-1 (mPGES-1), the enzyme generating PGE2, prevents blood-brain barrier P-gp up-regulation after status epilepticus (SE). To test our hypothesis, we exposed isolated brain capillaries to glutamate ex vivo and used a combined in vivo-ex vivo approach by isolating brain capillaries from humanized mPGES-1 mice to study P-gp levels. We demonstrate that glutamate signaling through the NMDA receptor, cytosolic phospholipase A2, COX-2, and mPGES-1 increases P-gp protein expression and transport activity levels. We show that mPGES-1 is expressed in human, rat, and mouse brain capillaries. We show that BI1029539, an mPGES-1 inhibitor, prevented up-regulation of P-gp expression and transport activity in capillaries exposed to glutamate and in capillaries from humanized mPGES-1 mice after SE. Our data provide key signaling steps underlying seizure-induced P-gp up-regulation and suggest that mPGES-1 inhibitors could potentially prevent P-gp up-regulation in epilepsy.-Soldner, E. L. B., Hartz, A. M. S., Akanuma, S.-I., Pekcec, A., Doods, H., Kryscio, R. J., Hosoya, K.-I., Bauer, B. Inhibition of human microsomal PGE2 synthase-1 reduces seizure-induced increases of P-glycoprotein expression and activity at the blood-brain barrier.

A Model of Chronic Temporal Lobe Epilepsy Presenting Constantly Rhythmic and Robust Spontaneous Seizures, Co-morbidities and Hippocampal Neuropathology

Many animal prototypes illustrating the various attributes of human temporal lobe epilepsy (TLE) are available. These models have been invaluable for comprehending multiple epileptogenic processes, modifications in electrophysiological properties, neuronal hyperexcitability, neurodegeneration, neural plasticity, and chronic neuroinflammation in TLE. Some models have also uncovered the efficacy of new antiepileptic drugs or biologics for alleviating epileptogenesis, cognitive impairments, or spontaneous recurrent seizures (SRS). Nonetheless, the suitability of these models for testing candidate therapeutics in conditions such as chronic TLE is debatable because of a lower frequency of SRS and an inconsistent pattern of SRS activity over days, weeks or months. An ideal prototype of chronic TLE for investigating novel therapeutics would need to display a large number of SRS with a dependable frequency and severity and related co-morbidities. This study presents a new kainic acid (KA) model of chronic TLE generated through induction of status epilepticus (SE) in 6-8 weeks old male F344 rats. A rigorous characterization in the chronic epilepsy period validated that the animal prototype mimicked the most salient features of robust chronic TLE. Animals displayed a constant frequency and intensity of SRS across weeks and months in the 5th and 6th month after SE, as well as cognitive and mood impairments. Moreover, SRS frequency displayed a rhythmic pattern with 24-hour periodicity and a consistently higher number of SRS in the daylight period. Besides, the model showed many neuropathological features of chronic TLE, which include a partial loss of inhibitory interneurons, reduced neurogenesis with persistent aberrant migration of newly born neurons, chronic neuroinflammation typified by hypertrophied astrocytes and rod-shaped microglia, and a significant aberrant mossy fiber sprouting in the hippocampus. This consistent chronic seizure model is ideal for investigating the efficacy of various antiepileptic drugs and biologics as well as understanding multiple pathophysiological mechanisms underlying chronic epilepsy.

Effect of carbamazepine on spontaneous recurrent seizures recorded from the dentate gyrus in rats with kainate-induced epilepsy

OBJECTIVE

Animal models of chronic epilepsy with spontaneous recurrent seizures (SRSs) may be useful in the discovery and mechanistic analyses of antiseizure drugs (ASDs). Carbamazepine (CBZ), a widely used ASD with a well-defined mechanism, was analyzed in this proof-of-principle study to determine how a traditional ASD affects the properties of SRSs.

METHODS

The effects of CBZ on electrographic SRSs recorded from the dentate gyrus were studied in freely behaving rats using a repeated, low-dose kainate model of acquired epilepsy with a repeated-measures, crossover protocol.

RESULTS

Almost all seizure durations were >20 seconds. Both seizure likelihood and duration appeared to be similar between 1 and 8 hours after individual CBZ injections. CBZ-induced decreases in seizure frequency were not significant at 10 mg/kg; however, at 30 mg/kg, seizure frequency was significantly reduced for convulsive but not nonconvulsive seizures. At 100 mg/kg, CBZ strongly suppressed both convulsive and nonconvulsive seizures. Although CBZ had a dose-dependent effect on seizure frequency, CBZ did not affect seizure duration at any dose. The preceding interictal interval did not affect seizure duration; however, at 30 mg/kg CBZ, nearly all seizures were nonconvulsive when the interictal interval was <30 minutes (ie, during clusters).

SIGNIFICANCE

Increased doses of CBZ (10-100 mg/kg) suppressed the frequency but not the duration of convulsive and nonconvulsive seizures in the repeated, low-dose kainate model. The repeated-measures, crossover protocol, which requires relatively few animals and compensates for progressive increases in seizure frequency during epileptogenesis after status epilepticus, allowed quantitative analyses of clinically relevant and translatable properties of SRSs.

The Pilocarpine Model of Temporal Lobe Epilepsy and EEG Monitoring Using Radiotelemetry System in Mice

Temporal lobe epilepsy (TLE) is a common neurological disorder in adulthood. For translational studies of chronic epilepsy, pilocarpine-induced status epilepticus (SE) is frequently selected to recapitulate spontaneous recurrent seizures (SRS). Here we present a protocol of SE induction by intraperitoneal (i.p.) injection of pilocarpine and monitoring of chronic recurring seizures in live animals using a wireless telemetry video and electroencephalogram (EEG) system. We demonstrated notable behavioral changes that need attention after pilocarpine injection and their correlation with hippocampal neuronal loss at 7 days and 6 weeks post-pilocarpine. We also describe the experimental procedures of electrode implantation for video and EEG recording, and analysis of the frequency and duration of chronic recurrent seizures. Finally, we discuss the possible reasons why the expected results are not achieved in each case. This provides a basic overview of modeling chronic epilepsy in mice and guidelines for troubleshooting. We believe this protocol can serve as a baseline for suitable models of chronic epilepsy and epileptogenesis.

Status Epilepticus: Behavioral and Electroencephalography Seizure Correlates in Kainate Experimental Models

Various etiological factors, such as head injury, chemical intoxication, tumors, and gene mutation, can induce epileptogenesis. In animal models, status epilepticus (SE) triggers epileptogenesis. In humans, convulsive SE for >30 min can be a life-threatening medical emergency. The duration and severity of convulsive SE are highly variable in chemoconvulsant animal models. A continuous video-electroencephalography (EEG) recording, and/or diligent direct observation, facilitates quantification of exact duration of different stages of convulsive seizures (Racine stages 3–5) to determine the severity of SE. A continuous convulsive SE for >30 min usually causes high mortality in some rodents and results in widespread brain damage in the surviving animals, in spite of treating with antiepileptic drugs (AEDs). AEDs control behavioral seizures but not EEG seizures. The severity of initial SE impacts epileptogenesis and cognitive function; therefore, quantitative assessment of behavioral SE and EEG in animal models will help to understand the impact of SE severity on epileptogenesis. There are several excellent reviews on experimental models of seizure/SE/epilepsy. This review focusses on the comparison of induction and characterization of behavioral SE and EEG correlates in mice and rats induced by kainate. We also discuss the advantages of repeated low dose of kainate (i.p. route), which minimizes variability in the initial SE severity between animals and reduces mortality rate. A refined approach to induce SE with kainate also addresses the two of the 3Rs (i.e., refinement and reduction), the guiding principles for ethical and scientific standpoint of animal research.

Effects of low-frequency electrical stimulation of the anterior piriform cortex on kainate-induced seizures in rats

OBJECTIVE

Recent evidence in animals and humans suggests that low-frequency stimulation (LFS) has significant antiepileptic properties. The anterior piriform cortex (APC) is a highly susceptible seizure-trigger zone and may be critical for the initiation and propagation of seizures originating from cortical and limbic foci. We used the kainic acid (KA) seizure model in rats to assess the therapeutic effect of LFS of the APC on seizures.

METHODS

Adult male Sprague-Dawley rats were implanted with electrodes in the left APC and recording electrodes bilaterally in the hippocampal CA3 regions. Rats were monitored continuously with video-EEG after the emergence of spontaneous recurrent seizures that followed induction of status epilepticus by intraperitoneal KA. After two weeks of baseline recordings to determine seizure frequency, LFS of the APC was applied 60-min On 15-min Off, for two weeks with 1Hz biphasic square waves, 0.2ms pulse width, at 200μA. Another 2-week period of video-EEG monitoring was done after the cessation of LFS to study the carry-over effect. Changes in seizure frequency, severity, and duration between baseline, during LFS, and post-LFS were analyzed using the Poisson regression model.

RESULTS

Overall seizure frequency decreased during the post-LFS period to 5% of that at baseline (p=0.003). Severe seizures (stages 4 and 5 on the Racine scale) decreased to 0% of the baseline during the post-LFS period.

CONCLUSIONS

Two weeks of LFS of the APC reduced spontaneous seizure frequency and severity in the KA model with the effect outlasting the stimulation. Our findings suggest that the APC can be an important therapeutic target for stimulation in epilepsy.

A novel animal model of acquired human temporal lobe epilepsy based on the simultaneous administration of kainic acid and lorazepam

OBJECTIVE

Kainic acid (KA) is a potent glutamate analog that is used to induce neurodegeneration and model temporal lobe epilepsy (TLE) in rodents. KA reliably induces severe, prolonged seizures, that is, convulsive status epilepticus (cSE), which is typically fatal without pharmacologic intervention. Although the use of KA to model human epilepsy has proven unquestionably valuable for >30 years, significant variability and mortality continue to confound results. These issues are probably the consequence of cSE, an all-or-nothing response that is inherently capricious and uncontrollable. The relevance of cSE to the human condition is dubious, however, as most patients with epilepsy never experienced it. We sought to develop a simple, KA-based animal model of TLE that avoids cSE and its confounds.

METHODS

Adult, male Sprague-Dawley rats received coincident subcutaneous injections of KA (5 mg) and lorazepam (0.25 mg), approximately 15.0 and 0.75 mg/kg, respectively. Continuous video-electroencephalography (EEG) was used to monitor acute seizure activity and detect spontaneous seizures. Immunocytochemistry, Fluoro-Jade B staining, and Timm staining were used to characterize both acute and chronic neuropathology.

RESULTS

Acutely, focal hippocampal seizures were induced, which began after about 30 min and were self-terminating after a few hours. Widespread hippocampal neurodegeneration was detected after 4 days. Spontaneous, focal hippocampal seizures began after an average of 12 days in all animals. Classic hippocampal sclerosis and mossy fiber sprouting characterized the long-term neuropathology. Morbidity and mortality rates were both 0%.

SIGNIFICANCE

We show here that the effects of systemic KA can be limited to the hippocampus simply with coadministration of a benzodiazepine at a low dose. This means that lorazepam can block convulsive seizures without truly stopping seizure activity. This novel, cSE-free animal model reliably mimics the defining characteristics of acquired mesial TLE: hippocampal sclerosis and spontaneous hippocampal-onset seizures after a prolonged seizure-free period, without significant morbidity, mortality, or nonresponders.

Anticonvulsant effects of antiaris toxicaria aqueous extract: investigation using animal models of temporal lobe epilepsy

BACKGROUND

Antiaris toxicaria has previously shown anticonvulsant activity in acute animal models of epilepsy. The aqueous extract (AAE) was further investigated for activity in kindling with pentylenetetrazole and administration of pilocarpine and kainic acid which mimic temporal lobe epilepsy in various animal species.

RESULTS

ICR mice and Sprague-Dawley rats were pre-treated with AAE (200-800 mg kg^-1) and convulsive episodes induced using pentylenetetrazole, pilocarpine and kainic acid. The potential of AAE to prevent or delay onset and alter duration of seizures were measured. In addition, damage to hippocampal cells was assessed in kainic acid-induced status epilepticus test. 800 mg kg^-1 of the extract suppressed the kindled seizure significantly (P < 0.05) as did diazepam. AAE also produced significant effect (P < 0.01) on latency to first myoclonic jerks and on total duration of seizures. The latency to onset of wet dog shakes was increased significantly (P < 0.05) by AAE on kainic acid administration. Carbamazepine and Nifedipine (30 mg kg^-1) also delayed the onset. Histopathological examination of brain sections showed no protective effect on hippocampal cells by AAE and nifedipine. Carbamazepine offered better preservation of hippocampal cells in the CA1, CA2 and CA3 regions.

CONCLUSION

Antiaris toxicaria may be effective in controlling temporal lobe seizures in rodents.

Acute and spontaneous seizure onset zones in the intraperitoneal kainic acid model

OBJECTIVE

Hippocampal monitoring is often used in the intraperitoneal kainic acid (KA) seizure model for detection and quantification of early ictal activity. Here, we investigated extra-hippocampal seizure onset zones (SOZs) in this model.

METHODS

Eight male Sprague Dawley rats implanted with depth electrodes were continuously recorded during intraperitoneal KA injections until status epilepticus (SE) was induced. Another group of four rats was monitored chronically up to two weeks after emergence of spontaneous recurrent seizures. All rats had hippocampal electrodes. Other sampled brain regions included, among others, the claustrum, piriform cortex, and orbital cortex. Seizures recorded with video-EEG were visually analyzed.

RESULTS

In the 58 seizures recorded during KA injections, the SOZ was extrahippocampal in 7 (12%), diffuse in 29 (50%), and hippocampal in 22 (38%). Of the 14 spontaneous seizures recorded, none were solely extrahippocampal, 10 (71%) were diffuse, and 4 (29%) were of hippocampal onset. All extra-hippocampal seizures propagated to the hippocampus within 4 to 50s (mean=14, n=7). No distinctive semiological manifestations correlated with the SOZs.

SIGNIFICANCE

We conclude that seizures can have multifocal SOZs in the KA model. This finding is important to consider when using this model, among other purposes, to screen for new therapies, study pharmacoresistance, or investigate comorbidities of epilepsy.

The Role of Sirt1 in Epileptogenesis

The mechanisms by which brain insults lead to subsequent epilepsy remain unclear. Insults, including trauma, stroke, tumors, infections, and long seizures [status epilepticus (SE)], create a neuronal state of increased metabolic demand or decreased energy supply. Neurons express molecules that monitor their metabolic state, including sirtuins (Sirts). Sirtuins deacetylate cytoplasmic proteins and nuclear histones, and their epigenetic modulation of the chromatin governs the expression of many genes, influencing neuronal properties. Thus, sirtuins are poised to enduringly modulate neuronal properties following SE, potentially contributing to epileptogenesis, a hypothesis supported by the epilepsy-attenuating effects of blocking a downstream target of Sirt1, Neuron-Restrictive Silencer Factor (NRSF) also know as REST (RE1-Silencing Transcription factor). Here we used an adult male rat model of epileptogenesis provoked by kainic acid-induced SE (KA-SE). We assessed KA-SE-provoked Sirt1 activity, infused a Sirt1 inhibitor (EX-527) after KA-SE, and examined for epileptogenesis using continuous digital video-EEG. Sirt1 activity, measured using chromatin immunoprecipitation for Sirt1 binding at a target gene, increased rapidly after SE. Post hoc infusion of the Sirt1 inhibitor prevented Sirt1-mediated repression of a target gene. Blocking Sirt1 activity transiently after KA-SE did not significantly influence the time- course and all of the parameters of epilepsy development. Specifically, latency to first seizure and seizure number, duration, and severity (using the Racine scale and EEG measures) as well as the frequency and duration of interictal spike series, were all unchanged. KA-SE provoked a robust inflammatory response and modest cell loss, yet neither was altered by blocking Sirt1. In conclusion, blocking Sirt1 activity after KA-SE does not abrogate epilepsy development, suggesting that the mechanisms of such acquired epileptogenesis are independent of Sirt1 function.

Metabolic injury in a variable rat model of post-status epilepticus

OBJECTIVE

In vivo studies of epilepsy typically use prolonged status epilepticus to generate recurrent seizures. However, reports on variable status duration have found discrete differences in injury after 40-50 min of seizures, suggesting a pathophysiologic sensitivity to seizure duration. In this report we take a multivariate cluster analysis to study a short duration status epilepticus model using in vivo 7T magnetic resonance spectroscopy (MRS) and histologic evaluation.

METHODS

The Hellier Dudek model was applied with 45 min of status epilepticus after which the animals were imaged twice, at 3 days and 3 weeks post-status epilepticus. Single voxel point resolved spectroscopy (PRESS) MRS was used to acquire data from the dentate gyrus and CA3 region of the hippocampus, assessing metabolite ratios to total creatine (tCr). In a subset of animals after the second imaging study, brains were analyzed histologically by Nissl staining.

RESULTS

A hierarchical cluster analysis performed on the 3-day data from 21 kainate-treated animals (dentate gyrus voxel) segregated into two clusters, denoted by KM (more injured, n = 6) and KL (less injured, n = 15). Although there was no difference in kainate dosing or seizure count between them, the metabolic pattern of injury was different. The KM group displayed the largest significant changes in neuronal and glial parameters; the KL group displayed milder but significant changes. At 3 weeks, the KL group returned to normal compared to controls, whereas the KM group persisted with depressed N-acetyl aspartate (NAA)/tCr, glutamate/tCr, and increased inositol/tCr and glutamine/tCr. The classification was also consistent with subsequent histologic patterns at 3 weeks.

SIGNIFICANCE

Although a short status period might be expected to generate a continuous distribution of metabolic injury, these data show that the short Hellier Dudek model appears to generate two levels of injury. The changes seen in segregated groups persisted into 3 weeks, and can be interpreted according to neuronal and glial biomarkers consistent with histology results.

Dual and Opposing Roles of MicroRNA-124 in Epilepsy Are Mediated through Inflammatory and NRSF-Dependent Gene Networks

Insult-provoked transformation of neuronal networks into epileptic ones involves multiple mechanisms. Intervention studies have identified both dysregulated inflammatory pathways and NRSF-mediated repression of crucial neuronal genes as contributors to epileptogenesis. However, it remains unclear how epilepsy-provoking insults (e.g., prolonged seizures) induce both inflammation and NRSF and whether common mechanisms exist. We examined miR-124 as a candidate dual regulator of NRSF and inflammatory pathways. Status epilepticus (SE) led to reduced miR-124 expression via SIRT1--and, in turn, miR-124 repression--via C/EBPα upregulated NRSF. We tested whether augmenting miR-124 after SE would abort epileptogenesis by preventing inflammation and NRSF upregulation. SE-sustaining animals developed epilepsy, but supplementing miR-124 did not modify epileptogenesis. Examining this result further, we found that synthetic miR-124 not only effectively blocked NRSF upregulation and rescued NRSF target genes, but also augmented microglia activation and inflammatory cytokines. Thus, miR-124 attenuates epileptogenesis via NRSF while promoting epilepsy via inflammation.

Seizure phenotypes, periodicity, and sleep-wake pattern of seizures in Kcna-1 null mice

This study was undertaken to describe seizure phenotypes, natural progression, sleep-wake patterns, as well as periodicity of seizures in Kcna-1 null mutant mice. These mice were implanted with epidural electroencephalography (EEG) and electromyography (EMG) electrodes, and simultaneous video-EEG recordings were obtained while animals were individually housed under either diurnal (LD) condition or constant darkness (DD) over ten days of recording. The video-EEG data were analyzed to identify electrographic and behavioral phenotypes and natural progression and to examine the periodicity of seizures. Sleep-wake patterns were analyzed to understand the distribution and onset of seizures across the sleep-wake cycle. Four electrographically and behaviorally distinct seizure types were observed. Regardless of lighting condition that animals were housed in, Kcna-1 null mice initially expressed only a few of the most severe seizure types that progressively increased in frequency and decreased in seizure severity. In addition, a circadian periodicity was noted, with seizures peaking in the first 12h of the Zeitgeber time (ZT) cycle, regardless of lighting conditions. Interestingly, seizure onset differed between lighting conditions where more seizures arose out of sleep in LD conditions, whereas under DD conditions, the majority occurred out of the wakeful state. We suggest that this model be used to understand the circadian pattern of seizures as well as the pathophysiological implications of sleep and circadian disturbances in limbic epilepsies.

Target-selectivity of parvalbumin-positive interneurons in layer II of medial entorhinal cortex in normal and epileptic animals

The medial entorhinal cortex layer II (MEClayerII ) is a brain region critical for spatial navigation and memory, and it also demonstrates a number of changes in patients with, and animal models of, temporal lobe epilepsy (TLE). Prior studies of GABAergic microcircuitry in MEClayerII revealed that cholecystokinin-containing basket cells (CCKBCs) select their targets on the basis of the long-range projection pattern of the postsynaptic principal cell. Specifically, CCKBCs largely avoid reelin-containing principal cells that form the perforant path to the ipsilateral dentate gyrus and preferentially innervate non-perforant path forming calbindin-containing principal cells. We investigated whether parvalbumin containing basket cells (PVBCs), the other major perisomatic targeting GABAergic cell population, demonstrate similar postsynaptic target selectivity as well. In addition, we tested the hypothesis that the functional or anatomic arrangement of circuit selectivity is disrupted in MEClayerII in chronic TLE, using the repeated low-dose kainate model in rats. In control animals, we found that PVBCs innervated both principal cell populations, but also had significant selectivity for calbindin-containing principal cells in MEClayerII . However, the magnitude of this preference was smaller than for CCKBCs. In addition, axonal tracing and paired recordings showed that individual PVBCs were capable of contacting both calbindin and reelin-containing principal cells. In chronically epileptic animals, we found that the intrinsic properties of the two principal cell populations, the GABAergic perisomatic bouton numbers, and selectivity of the CCKBCs and PVBCs remained remarkably constant in MEClayerII . However, miniature IPSC frequency was decreased in epilepsy, and paired recordings revealed the presence of direct excitatory connections between principal cells in the MEClayerII in epilepsy, which is unusual in normal adult MEClayerII . Taken together, these findings advance our knowledge about the organization of perisomatic inhibition both in control and in epileptic animals. © 2015 Wiley Periodicals, Inc.

Metabolic changes in early poststatus epilepticus measured by MR spectroscopy in rats

There is little experimental in vivo data on how differences in seizure duration in experimental status epilepticus influence metabolic injury. This is of interest given that in humans, status duration is a factor that influences the probability of subsequent development of epilepsy. This question is studied using 7-T magnetic resonance (MR) spectroscopy, T2 relaxometry in the incremented kainate rodent model of temporal lobe epilepsy, using two durations of status epilepticus, 1.5 and 3 hours. Histologic evaluation was performed in a subset of animals. Three days after status, single-voxel (8 mm(3)) point resolved spectroscopy (PRESS) MR spectroscopic measurements were acquired at 7 T to assess the cerebral metabolites measured as a ratio to total creatine (tCr). The status injury resulted in decreased N-acetylaspartate NAA/tCr, increased myo-inositol/tCr and glutamine/tCr, increased T2, and significant declines in NeuN-stained neuronal counts in both status groups. Regressions were identified in the status groups that provide evidence for neuronal injury and astrocytic reaction after status in both the short and long status duration groups. The long status group displays changes in glutathione/tCr that are not identified in the short status group, this difference possibly representing a maturation of injury and antioxidant response that occurs in synchrony with glutamatergic injury and glial activation.

Neonatal seizures alter NMDA glutamate receptor GluN2A and 3A subunit expression and function in hippocampal CA1 neurons

Neonatal seizures are commonly caused by hypoxic and/or ischemic injury during birth and can lead to long-term epilepsy and cognitive deficits. In a rodent hypoxic seizure (HS) model, we have previously demonstrated a critical role for seizure-induced enhancement of the AMPA subtype of glutamate receptor (GluA) in epileptogenesis and cognitive consequences, in part due to GluA maturational upregulation of expression. Similarly, as the expression and function of the N-Methyl-D-aspartate (NMDA) subtype of glutamate receptor (GluN) is also developmentally controlled, we examined how early life seizures during the critical period of synaptogenesis could modify GluN development and function. In a postnatal day (P)10 rat model of neonatal seizures, we found that seizures could alter GluN2/3 subunit composition of GluNs and physiological function of synaptic GluNs. In hippocampal slices removed from rats within 48–96 h following seizures, the amplitudes of synaptic GluN-mediated evoked excitatory postsynaptic currents (eEPSCs) were elevated in CA1 pyramidal neurons. Moreover, GluN eEPSCs showed a decreased sensitivity to GluN2B selective antagonists and decreased Mg²⁺ sensitivity at negative holding potentials, indicating a higher proportion of GluN2A and GluN3A subunit function, respectively. These physiological findings were accompanied by a concurrent increase in GluN2A phosphorylation and GluN3A protein. These results suggest that altered GluN function and expression could potentially contribute to future epileptogenesis following neonatal seizures, and may represent potential therapeutic targets for the blockade of future epileptogenesis in the developing brain.

Rapid brief feedback intracerebral stimulation based on real-time desynchronization detection preceding seizures stops the generation of convulsive paroxysms

OBJECTIVE

To investigate the abortion of seizure generation using "minimal" intervention in hippocampi using two rat models of human temporal lobe epilepsy.

METHODS

The recording or stimulation electrodes were implanted into both hippocampi (CA1 area). Using the kainic acid (chronic: experiment duration 24 days) and the 4-aminopyridine (acute: experiment duration 2 h) models of paroxysms in rats, a real-time feedback stimulation paradigm was implemented, which triggered a short periodic electrical stimulus (5 Hz for 5 s) upon detecting a seizure precursor. Our seizure precursor detection algorithm relied on the monitoring of the real-time phase synchronization analysis, and detected/anticipated electrographic seizures as early as a few seconds to a few minutes before the behavioral and electrographic seizure onset, with a very low false-positive rate of the detection.

RESULTS

The baseline mean seizure frequencies were 5.39 seizures per day (chronic) and 13.2 seizures per hour (acute). The phase synchrony analysis detected 88% (434 of 494) of seizures with a mean false alarm of 0.67 per day (chronic) and 83% (86 of 104) of seizures with a mean false alarm of 0.47 per hour (acute). The feedback stimulation reduced the seizure frequencies to 0.41 seizures per day (chronic) and 2.4 seizures per hour (acute). Overall, the feedback stimulation paradigm reduced seizure frequency by a minimum of 80% to a maximum of 100% in 10 rats, with 83% of the animals rendered seizure-free.

SIGNIFICANCE

This approach represents a simple and efficient manner for stopping seizure development. Because of the short on-demand stimuli, few or no associated side effects are expected in clinical application in patients with epilepsy. Abnormal synchrony patterns are common features in epilepsy and other neurologic and psychiatric syndromes; therefore, this type of feedback stimulation paradigm could be a novel therapeutic modality for use in various neurologic and psychiatric disorders.

Complex metabolically demanding sensory processing in the olfactory system: implications for epilepsy

Although the olfactory system is not generally associated with seizures, sharp application of odor eliciting activity in a large number of olfactory sensory neurons (OSNs) has been shown to elicit seizures. This is most likely due to increased ictal activity in the anterior piriform cortex-an area of the olfactory system that has limited GABAergic interneuron inhibition of pyramidal output cell activity. Such hyperexcitability in a well-characterized and highly accessible system makes olfaction a potentially powerful model system to examine epileptogenesis.

Advantages of repeated low dose against single high dose of kainate in C57BL/6J mouse model of status epilepticus: behavioral and electroencephalographic studies

A refined kainate (KA) C57BL/6J mouse model of status epilepticus (SE) using a repeated low dose (RLD) of KA (5 mg/kg, intraperitoneal; at 30 min intervals) was compared with the established single high dose (SHD) of KA (20 mg/kg, intraperitoneal) model. In the RLD group, increased duration of convulsive motor seizures (CMS, Racine scale stage ≥3) with a significant reduction in mortality from 21% to 6% and decreased variability in seizure severity between animals/batches were observed when compared to the SHD group. There was a significant increase in the percentage of animals that reached stage-5 seizures (65% versus 96%) in the RLD group. Integrated real-time video-EEG analysis of both groups, using NeuroScore software, revealed stage-specific spikes and power spectral density characteristics. When the seizures progressed from non-convulsive seizures (NCS, stage 1-2) to CMS (stage 3-5), the delta power decreased which was followed by an increase in gamma and beta power. A transient increase in alpha and sigma power marked the transition from NCS to CMS with characteristic 'high frequency trigger' spikes on the EEG, which had no behavioral expression. During SE the spike rate was higher in the RLD group than in the SHD group. Overall these results confirm that RLD of KA is a more robust and consistent mouse model of SE than the SHD of KA mouse model.

Domoic acid epileptic disease

Domoic acid epileptic disease is characterized by spontaneous recurrent seizures weeks to months after domoic acid exposure. The potential for this disease was first recognized in a human case study of temporal lobe epilepsy after the 1987 amnesic shellfish-poisoning event in Quebec, and was characterized as a chronic epileptic syndrome in California sea lions through investigation of a series of domoic acid poisoning cases between 1998 and 2006. The sea lion study provided a breadth of insight into clinical presentations, unusual behaviors, brain pathology, and epidemiology. A rat model that replicates key observations of the chronic epileptic syndrome in sea lions has been applied to identify the progression of the epileptic disease state, its relationship to behavioral manifestations, and to define the neural systems involved in these behavioral disorders. Here, we present the concept of domoic acid epileptic disease as a delayed manifestation of domoic acid poisoning and review the state of knowledge for this disease state in affected humans and sea lions. We discuss causative mechanisms and neural underpinnings of disease maturation revealed by the rat model to present the concept for olfactory origin of an epileptic disease; triggered in dendodendritic synapases of the olfactory bulb and maturing in the olfactory cortex. We conclude with updated information on populations at risk, medical diagnosis, treatment, and prognosis.

The kainic acid model of temporal lobe epilepsy

The kainic acid model of temporal lobe epilepsy has greatly contributed to the understanding of the molecular, cellular and pharmacological mechanisms underlying epileptogenesis and ictogenesis. This model presents with neuropathological and electroencephalographic features that are seen in patients with temporal lobe epilepsy. It is also characterized by a latent period that follows the initial precipitating injury (i.e., status epilepticus) until the appearance of recurrent seizures, as observed in the human condition. Finally, the kainic acid model can be reproduced in a variety of species using either systemic, intrahippocampal or intra-amygdaloid administrations. In this review, we describe the various methodological procedures and evaluate their differences with respect to the behavioral, electroencephalographic and neuropathological correlates. In addition, we compare the kainic acid model with other animal models of temporal lobe epilepsy such as the pilocarpine and the kindling model. We conclude that the kainic acid model is a reliable tool for understanding temporal lobe epilepsy, provided that the differences existing between methodological procedures are taken into account.

Dual leucine zipper kinase is required for excitotoxicity-induced neuronal degeneration

Loss of dual leucine zipper kinase results in attenuated JNK/c-Jun stress response pathway activation and reduced neuronal degeneration after kainic acid–induced excitotoxic seizures.

Excessive glutamate signaling is thought to underlie neurodegeneration in multiple contexts, yet the pro-degenerative signaling pathways downstream of glutamate receptor activation are not well defined. We show that dual leucine zipper kinase (DLK) is essential for excitotoxicity-induced degeneration of neurons in vivo. In mature neurons, DLK is present in the synapse and interacts with multiple known postsynaptic density proteins including the scaffolding protein PSD-95. To examine DLK function in the adult, DLK-inducible knockout mice were generated through Tamoxifen-induced activation of Cre-ERT in mice containing a floxed DLK allele, which circumvents the neonatal lethality associated with germline deletion. DLK-inducible knockouts displayed a modest increase in basal synaptic transmission but had an attenuation of the JNK/c-Jun stress response pathway activation and significantly reduced neuronal degeneration after kainic acid–induced seizures. Together, these data demonstrate that DLK is a critical upstream regulator of JNK-mediated neurodegeneration downstream of glutamate receptor hyper-activation and represents an attractive target for the treatment of indications where excitotoxicity is a primary driver of neuronal loss.

Specific imaging of inflammation with the 18 kDa translocator protein ligand DPA-714 in animal models of epilepsy and stroke

Inflammation is a pathophysiological hallmark of many diseases of the brain. Specific imaging of cells and molecules that contribute to cerebral inflammation is therefore highly desirable, both for research and in clinical application. The 18 kDa translocator protein (TSPO) has been established as a suitable target for the detection of activated microglia/macrophages. A number of novel TSPO ligands have been developed recently. Here, we evaluated the high affinity TSPO ligand DPA-714 as a marker of brain inflammation in two independent animal models. For the first time, the specificity of radiolabeled DPA-714 for activated microglia/macrophages was studied in a rat model of epilepsy (induced using Kainic acid) and in a mouse model of stroke (transient middle cerebral artery occlusion, tMCAO) using high-resolution autoradiography and immunohistochemistry. Additionally, cold-compound blocking experiments were performed and changes in blood-brain barrier (BBB) permeability were determined. Target-to-background ratios of 2 and 3 were achieved in lesioned vs. unaffected brain tissue in the epilepsy and tMCAO models, respectively. In both models, ligand uptake into the lesion corresponded well with the extent of Ox42- or Iba1-immunoreactive activated microglia/macrophages. In the epilepsy model, ligand uptake was almost completely blocked by pre-injection of DPA-714 and FEDAA1106, another high-affinity TSPO ligand. Ligand uptake was independent of the degree of BBB opening and lesion size in the stroke model. We provide further strong evidence that DPA-714 is a specific ligand to image activated microglia/macrophages in experimental models of brain inflammation.

Diphenytoin, riluzole and lidocaine: three sodium channel blockers, with different mechanisms of action, decrease hippocampal epileptiform activity

Epilepsy is a condition affecting 1-2% of the population, characterized by the presence of spontaneous, recurrent seizures. The most common type of acquired epilepsy is temporal lobe epilepsy (TLE). Up to 30% of patients with TLE are refractory to currently available compounds, and there is an urgent need to identify novel targets for therapy. Here, we utilized the in-vitro CA3 burst preparation to examine alterations in network excitability, characterized by changes in interburst interval. Specifically, we show that bath application of three different sodium channel blockers-diphenytoin, riluzole, and lidocaine-slow spontaneous CA3 bursts. This in turn, decreased the epileptiform activity. These compounds work at different sites on voltage-gated sodium channels, but produce a similar network phenotype of decreased excitability. In the case of diphenytoin and riluzole, the change in network activity (i.e., increased interburst intervals) was persistent following drug washout. Lidocaine application, however, only increased the CA3 interburst interval when it was in the bath solution. Thus, its action was not permanent and resulted in returning CA3 bursting to baseline levels. These data demonstrate that the CA3 burst preparation provides a relatively easy and quick platform for identifying compounds that can decrease network excitability, providing the initial screen for further and more complex in-vivo, freely-behaving animal studies.

A Cupric Silver Histochemical Analysis of Domoic Acid Damage to Olfactory Pathways Following Status Epilepticus in a Rat Model for Chronic Recurrent Spontaneous Seizures and Aggressive Behavior

The amnesic shellfish toxin, domoic acid, interferes with glutamatergic pathways leading to neuronal damage, most notably causing memory loss and seizures. In this study, the authors utilized a recently developed rat model for domoic acid–induced epilepsy, an emerging disease appearing in California sea lions weeks to months after poisoning, to identify structural damage that may lead to a permanent epileptic state. Sprague Dawley rats were kindled with several low hourly intraperitoneal doses of domoic acid until a state of status epilepticus (SE) appears. This kindling approach has previously been shown to induce a permanent state of epileptic disease in 96% animals within 6 months. Three animals were selected for neurohistology a week after the initial SE. An amino cupric silver staining method using neutral red counterstain was used on every eighth 40 µm coronal section from each brain to highlight neural degeneration from the olfactory bulb through the brain stem. The most extensive damage was found in the olfactory bulb and related olfactory pathways, including the anterior/medial olfactory cortices, endopiriform nucleus, and entorhinal cortex. These findings indicate that damage to olfactory pathways is prominent in a rat model for domoic acid–induced chronic recurrent spontaneous seizures and aggressive behavior.

Prenatal choline deficiency does not enhance hippocampal vulnerability after kainic acid-induced seizures in adulthood

Choline is a vital nutrient needed during early development for both humans and rodents. Severe dietary choline deficiency during pregnancy leads to birth defects, while more limited deficiency during mid- to late pregnancy causes deficits in hippocampal plasticity in adult rodent offspring that are accompanied by cognitive deficits only when task demands are high. Because prenatal choline supplementation confers neuroprotection of the adult hippocampus against a variety of neural insults and aids memory, we hypothesized that prenatal choline deficiency may enhance vulnerability to neural injury. To examine this, adult offspring of rat dams either fed a control diet (CON) or one deficient in choline (DEF) during embryonic days 12-17 were given multiple injections (i.p.) of saline (control) or kainic acid to induce seizures and were euthanized 16 days later. Perhaps somewhat surprisingly, DEF rats were not more susceptible to seizure induction and showed similar levels of seizure-induced hippocampal histopathology, GAD expression loss, upregulated hippocampal GFAP and growth factor expression, and increased dentate cell and neuronal proliferation as that seen in CON rats. Although prenatal choline deficiency compromises adult hippocampal plasticity in the intact brain, it does not appear to exacerbate the neuropathological response to seizures in the adult hippocampus at least shortly after excitotoxic injury.

Domoic acid induced seizures progress to a chronic state of epilepsy in rats

The emergence of an epilepsy syndrome in sea lions poisoned by domoic acid (DA) draws striking parallels to the single case study of temporal lobe epilepsy (TLE) that developed in an 84 yr old man one year after being poisoned by DA. To establish a basis for understanding this disease in sea lions and humans that appears to progress from DA poisoning, we have investigated the potential for a single incident of DA poisoning in rats to progress to spontaneous recurrent seizures (SRS), the hallmark of epilepsy. We have developed a DA administration protocol to induce a nonlethal status epilepticus (SE) and monitored the animals for SRS by 6 h/week of video recording. We demonstrate that a single episode of SE leads to SRS in 94% of rats (n = 23) in 6 months. These findings indicate that DA induced SE can efficiently translate to epileptic disease.

Water maze experience and prenatal choline supplementation differentially promote long-term hippocampal recovery from seizures in adulthood

Status epilepticus (SE) in adulthood dramatically alters the hippocampus and produces spatial learning and memory deficits. Some factors, like environmental enrichment and exercise, may promote functional recovery from SE. Prenatal choline supplementation (SUP) also protects against spatial memory deficits observed shortly after SE in adulthood, and we have previously reported that SUP attenuates the neuropathological response to SE in the adult hippocampus just 16 days after SE. It is unknown whether SUP can ameliorate longer-term cognitive and neuropathological consequences of SE, whether repeatedly engaging the injured hippocampus in a cognitive task might facilitate recovery from SE, and whether our prophylactic prenatal dietary treatment would enable the injured hippocampus to more effectively benefit from cognitive rehabilitation. To address these issues, adult offspring from rat dams that received either a control (CON) or SUP diet on embryonic days 12-17 first received training on a place learning water maze task (WM) and were then administered saline or kainic acid (KA) to induce SE. Rats then either remained in their home cage, or received three additional WM sessions at 3, 6.5, and 10 weeks after SE to test spatial learning and memory retention. Eleven weeks after SE, the brains were analyzed for several hippocampal markers known to be altered by SE. SUP attenuated SE-induced spatial learning deficits and completely rescued spatial memory retention by 10 weeks post-SE. Repeated WM experience prevented SE-induced declines in glutamic acid decarboxylase (GAD) and dentate gyrus neurogenesis, and attenuated increased glial fibrilary acidic protein (GFAP) levels. Remarkably, SUP alone was similarly protective to an even greater extent, and SUP rats that were water maze trained after SE showed reduced hilar migration of newborn neurons. These findings suggest that prophylactic SUP is protective against the long-term cognitive and neuropathological effects of KA-induced SE, and that rehabilitative cognitive enrichment may be partially beneficial.

Development of spontaneous recurrent seizures after kainate-induced status epilepticus

Acquired epilepsy (i.e., after an insult to the brain) is often considered to be a progressive disorder, and the nature of this hypothetical progression remains controversial. Antiepileptic drug treatment necessarily confounds analyses of progressive changes in human patients with acquired epilepsy. Here, we describe experiments testing the hypothesis that development of acquired epilepsy begins as a continuous process of increased seizure frequency (i.e., proportional to probability of a spontaneous seizure) that ultimately plateaus. Using nearly continuous surface cortical and bilateral hippocampal recordings with radiotelemetry and semiautomated seizure detection, the frequency of electrographically recorded seizures (both convulsive and nonconvulsive) was analyzed quantitatively for approximately 100 d after kainate-induced status epilepticus in adult rats. The frequency of spontaneous recurrent seizures was not a step function of time (as implied by the "latent period"); rather, seizure frequency increased as a sigmoid function of time. The distribution of interseizure intervals was nonrandom, suggesting that seizure clusters (i.e., short interseizure intervals) obscured the early stages of progression, and may have contributed to the increase in seizure frequency. These data suggest that (1) the latent period is the first of many long interseizure intervals and a poor measure of the time frame of epileptogenesis, (2) epileptogenesis is a continuous process that extends much beyond the first spontaneous recurrent seizure, (3) uneven seizure clustering contributes to the variability in occurrence of epileptic seizures, and (4) the window for antiepileptogenic therapies aimed at suppressing acquired epilepsy probably extends well past the first clinical seizure.

NMDA receptor-mediated long-term alterations in epileptiform activity in experimental chronic epilepsy

When epileptiform activity is acutely induced in vitro, transient partial blockade of N-methyl-d-aspartic acid (NMDA) receptor-mediated calcium influx leads to selective long-term depotentiation of the synapses involved in the epileptic activity as well as a reduction in the probability of further epileptiform activity. If such selective depotentiation occurred within foci of epileptic activity in vivo, the corresponding long-term reduction in seizure probability could form the basis for a novel treatment of epilepsy. Continuous radiotelemetric EEG monitoring demonstrated modest acute anticonvulsant effects but no long-term reductions in the probability of spontaneous seizures after transient partial blockade of NMDA receptors (NMDAR) during ictal and interictal activity in the kainate animal model of chronic epilepsy. In vitro, depotentiation was induced when NMDAR were partially blocked during epileptiform activity in hippocampal slices from control animals, but not in slices from chronically epileptic rats. However in slices from epileptic animals, depotentiation during epileptiform activity was induced by partial block of NMDAR using NR2B- but not NR2A-selective antagonists. These results suggest that chronic epileptic activity is associated with changes in NMDA receptor-mediated signaling that is reflected in the pharmacology of activity- and NMDA receptor-dependent depotentiation.